ADA4522-4ARZ-R7 datasheet(35/48 Pages) AD

35 / 48 page

Data Sheet

ADA4522-1/ADA4522-

2/ADA4522-4

analog.com

Rev I 35 of 48

Current Noise Density

Figure 78

shows the current noise density of the ADA4522-1/ADA4522-2/ADA4522-4 at unity gain. At 1 kHz, the current

noise density is about 1.3 pA/√Hz. The current noise density is determined by measuring the voltage noise due to

current noise flowing through a resistor. Due to the low current noise density of the amplifier, the voltage noise is

usually measured with a high value resistor; in this case, a 100 kΩ source resistor is used. However, the source resistor

interacts with the input capacitance of the amplifier and board, causing the bandwidth to roll off. Note that Figure

shows the current noise density rolling off much earlier than the unity-gain bandwidth; this roll-off is expected.

Figure 78.Current Noise Density at Gain = 1

EMI Rejection Ratio

Circuit performance is often adversely affected by high frequency EMI. When the signal strength is low and

transmission lines are long, an op amp must accurately amplify the input signals. However, all op amp pins—the

noninverting input, inverting input, positive supply, negative supply, and output pins—are susceptible to EMI signals.

These high frequency signals are coupled into an op amp by various means, such as conduction, near field radiation,

or far field radiation. For example, wires and printed circuit board (PCB) traces can act as antennas and pick up high

frequency EMI signals.

Amplifiers do not amplify EMI or RF signals due to their relatively low bandwidth. However, due to the nonlinearities

of the input devices, op amps can rectify these out of band signals. When these high frequency signals are rectified,

they appear as a DC offset at the output.

The ADA4522-1/ADA4522-2/ADA4522-4 have integrated EMI filters at their input stage. To describe the ability of the

ADA4522-1/ADA4522-2/ADA4522-4 to perform as intended in the presence of electromagnetic energy, the

electromagnetic interference rejection ratio (EMIRR) of the noninverting pin is specified in Table 2, Table 3, and Table

of the Specifications section. A mathematical method of measuring EMIRR is defined as follows:

EMIRR = 20log(VIN_PEAK/ΔVOS)

(5)

0.1

100

10k

100k

FREQUENCY (Hz)

VSY = ±2.5V

VSY = ±15V

VSY = ±27.5V

RS = 100kΩ

AV = 1

ADA4522-4ARZ-R7 Datasheet(PDF) 35 Page - Analog Devices